“the great question of life, the universe and everything” dr. véronique boisvert royal...
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“The Great Question of Life, the Universe and Everything”“The Great Question of Life,
the Universe and Everything”
Dr. Véronique Boisvert
Royal Holloway, University of London
A lot of the following pictures come from: www.particleadventure.org
Every day ParticlesEvery day Particles
All of biology, chemistry and 95% of physics make use of 4 particles!
Quarks and LeptonsQuarks and Leptons
Mesons: quark + anti-quark: K0 (sd)
Baryons: 3 quarks: p (uud), n(udd), (usd)
Gravity?Gravity?
• Force carrier: graviton?• Very long range• Einstein: property of space-time (General Relativity)
• Been trying to unify with quantum mechanics for 75 years!
The Standard ModelThe Standard Model
• Very successful model• No discrepancy so far
• But incomplete!• Neutrino mass!• Why 3 generations?• Why Universe is mostly
matter?• Where do the mass of
particles come from?
The Higgs bosonThe Higgs boson
• Electroweak symmetry is exact only if W,Z are massless: so symmetry broken?
• Not quite: the physical vacuum is not unique• Higgs field might be responsible?
Re(Higgs Field)
Im(Higgs Field)
Potential Energy
The Higgs field and bosonThe Higgs field and boson
Higgs field mechanism
Higgs boson
CERN © and inspired by David J. Miller at UCL
How do we know what we know? Method 1
How do we know what we know? Method 1
De Broglie : Wave-Particle Duality
€
λ= h / p
nucleus
nucleon
quark
10-14 m 10-16 m 10-18 m
quark
?
wavelength momentum
Planck’s constant
Einstein : Mass Energy Equivalence
€
E = mc 2
energy speed-of-light
mass
How do we know what we know? Method 2
How do we know what we know? Method 2
• We can take the subtle approach: make precision measurements
• Example: b quark turns into an s quark• Only happens if there is a “loop” of
virtual quarks• Since we don’t observe these quarks
in the loop, all quarks will participate• Rate of this reaction proportional to
mass of the quarks• First (indirect) detection of the top quark!
AcceleratorsAccelerators
• Step 1: Get the particles you want to accelerate
• Step 2: Accelerate them using electromagnetic radiation
AcceleratorsAccelerators
• Linac: can reach 25MeV/m • Would need 40km to
reach 1000GeV!
SLAC
• Cyclotron: uses circular path!• p=0.3Bq• Bq/m• If particle reaches relativistic v: gets out
of phase!
AcceleratorsAccelerators
• Synchrotrons: keep varying the magnetic field and synchronize the accelerating cavities
Tevatron at FNAL (method 1)
PEP-II at SLAC Center of mass E = 10.58GeV
(method 2)
The Large Hadron ColliderThe Large Hadron Collider
World’s biggest ever scientific undertaking!
15 years to build : data taking starts this year!
The Large Hadron Collider
• 9300 magnets along the ring• Magnets are precooled to -193.2°C (80 K)
using 10 080 tons of liquid nitrogen• before they are filled with nearly 60 tons
of liquid helium to bring them down to -271.3°C (1.9 K)• Cooler than outer space!
• Radiofrequency cavities:• Accelerate the beam of particles
• Vacuum chambers:• Beam pipe under high vacuum to
prevent collisions with air
• Magnets:• Dipole, quadrupoles, etc.
Center of Mass EnergyCenter of Mass Energy
• 7 TeV proton beam colliding with 7 TeV proton beam = 14 TeV available
• TeV = Tera (1012) electronVolt• 1 electronvolt
• E of 1 electron under a potential difference of 1 Volt• E=qV = (1.602x10-19C)(1V) = 1.602x10-19J
• So 14TeV = 2.23 x 10-6 J (1J: E released when an apple falls 1m)
• Trick is: we use the energy to make particles!• E=mc2 in SI units: 2.23x10-6J = m (3x108m/s)2
• m = 2.48x10-23 Kg • m of p: 1.67x10-27Kg (938 MeV), m of heaviest particle (top quark):
3.06x10-25Kg (172 GeV)• So 80 times heavier than currently heaviest particle!
Lepton vs hadron collidersLepton vs hadron colliders
• Why 14TeV?• Since colliding protons
with protons• Not all the proton E
available in the quark or gluon collision
• With 14 TeV about 1-2 TeV will be available for new particles
proton proton
• Inelastic collisions with the atomic electrons of the material
• ionization
energy loss (Bethe-Bloch equation)
•Elastic collisions with the nuclei of the material
• displacement of the atom
• change of trajectory
• also Bremstrahlung
• deflection of e+/e- because of electric field from nucleus acceleration change radiation
Particles Interactions with matter
Particles Interactions with matter
Charged Particles (p+, ±, …)
e+/e- ()
• Low Energy:
• elastic and inelastic collision, capture, fission
• Higher Energy (relevant to HEP):
• high energy hadron shower production
Photons (X, , …)
Neutral Particles (n, 0, KS/L,…)
DetectorsDetectors
• ATLAS Silicon Pixel Detector• Closest to the beam pipe• Charged tracks ionize the silicon• Each pixel is 50 x 300 • 140million of them!
• ATLAS Electromagnetic Calorimeter•Measures energy of photons and electrons•Layers of Lead: incoming particles make showers of secondary particles•Sensing material: liquid argon gets ionized by shower of particle•Amount of charge collected proportional to E of incoming particle
DetectorsDetectors
• When the LHC turns on there will be a rate of 40 million events per second!
• Most of these are uninteresting events, we want to keep about 100 events per second• The Trigger:
• Use signatures of interesting events to decide whether to keep the event or not
• Use both hardware and software algorithms
40 MHz
75 kHz
~1 kHz
~100 Hz
~1 sec
~10 ms
2.5 s
Rate Latency
Reconstructing the eventsReconstructing the events
• Even interesting events are very busy:• ~ 100 particles per event• Most of them are not
related with the interesting part of the event
• Need sophisticated software
• to reconstruct the event• to extract the physics
out of the event
The Computing ChallengeThe Computing Challenge
10 million Gbytes of data per year100,000 PCs needed to analyse it!
How would you do an analysis?How would you do an analysis?
• Step 1: Pick a topic!• Which mystery do you want to elucidate?• Is the time scale of the experiment
appropriate?• How “crowded” is this topic?
How would you do an analysis?How would you do an analysis?
• Step 2: Design the selection of the events of interest• Use Monte Carlo simulations• The selection will be done by
computing algorithms (C++)• You need to optimize:
• Want as many signal events as possible (reduce statistical uncertainties!)
• Want as low backgrounds as possible (reduce systematic uncertainties!)
How would you do an analysis?How would you do an analysis?
• Step 3: run on the data• “counting” experiment:
• count number of signal events• Count signal events that look like this vs look like that
• “fitting” experiment: fit a distribution to get number of events or a parameter: a mass for example
€
MH = mγγ = 2Eγ 1Eγ 2
(1− cosθγ 1γ 2)
Now you try it: http://lppp.lancs.ac.uk/higgs/index.html
What will we find???What will we find???Supersymmetry? Extra Spatial Dimensions ?
Mini black holes?
?
The unexpected ?
ATLAS the CollaborationATLAS the Collaboration
• Make use of virtual tools to communicate• WWW was invented at
CERN!
• 37 countries• 1850 physicists• Many languages!
Particle Physics @ RHULParticle Physics @ RHUL
• Very strong and established group• Was involved on ALEPH• Ramping down on BaBar
• Looking toward the future• Well established group on ATLAS
• Built part of the Data Acquisition System• Designed and implemented significant parts of the High Level
Trigger• Currently: 4 faculty, 6 RA/Engineer, 8 PhD• Covering all interesting physics: Higgs, SUSY, Exotics, Top
quark
• Linear Collider Work : Part of John Adams Institute• 4 faculty, 4 RA, 4 PhD• Beam monitoring as well as detector R&D